The present invention relates to an optical object identification device and a printing apparatus using the same, and more particularly to an optical object identification device for detecting information on a paper form in a noncontact way so as to improve printing quality by optimizing a quantity of ink in an ink jet printer or the like, and to a printing apparatus using the same.
In a first conventional optical object identification device, as shown in FIG. 7, a light emission element 31 and a photodetector 32 are provided so as to form a specified angle with a paper form 33. In the first conventional optical object identification device, light emitted from the light emission element 31 is reflected by the paper form 33, and then part of the reflected light is made incident on the photodetector 32. In this situation, a quantity of the light incident on the photodetector 32 differs according to a type (a surface condition) of the paper form 33. The paper form 33 is therefore identified on basis of the difference in the light quantity.
In a second conventional optical object identification device, as shown in FIG. 8, one light emission element 34 and two photodetectors 35 and 36 are provided so as to form specified angles with a plane surface of a paper form 37. In the second conventional optical object identification device, two photodetectors are provided for receiving light that is reflected spectrally and light that is reflected diffusely from the paper form 33, respectively. The paper form is identified on basis of a difference between quantities of light incident on the two photodetectors 35 and 36 which difference varies according to paper forms.
The first and second conventional optical object identification devices are composed of one light emission unit and one photodetector unit or are composed of one light emission unit and a plurality of photodetector units. Each unit is positioned so as to form a specified angle with a plane surface of a paper form, and the devices identify paper forms on basis of the difference in quantity of light reflected from the paper forms.
However, the devices have a problem in that it is difficult to identify paper forms correctly because the quantity of the reflected light varies with a quantity of light in the light emission unit, sensitivity of the photodetector units, variation in surface condition of paper forms, variation in relation among positions of the light emission unit, the photodetector units, and a paper form. Plain paper, glossy paper, photo glossy paper and OHP paper are used for paper forms. It is difficult to make identification between plain paper and glossy paper with satisfactory repeatability, while it is relatively easy to make identification other than the identification between plain paper and glossy paper.